Early gx/rx session failure detection and response

ABSTRACT

A network gateway can prevent a new communication session for a user equipment (UE) from failing by establishing Diameter Gx session binding with a backup Policy Control Function (PCF) when a Gx session cannot be established between the gateway and a primary PCF. The gateway and the primary PCF may be associated with the same network generation (such as LTE or 5G), and the backup PCF can be associated with a different network generation. An IP Multimedia Subsystem (IMS) can determine that Gx binding information about the UE is not available at the primary PCF. However, to prevent failure of the new communication session for the UE, the IMS can cause the backup PCF to use its Gx binding information to identify the Gx session established with the network gateway for the UE and provide the network gateway with rules for the new communication session.

BACKGROUND

In a telecommunication network, Diameter protocol interfaces can link aPolicy Control Function (PCF), such as a Policy and Charging RulesFunction (PCRF), with gateways of a core network as well as withelements of an IP Multimedia Subsystem (IMS). For example, a PCRF can belinked over a Diameter Gx interface with a Packet Data Network Gateway(P-GW) of a Long Term Evolution (LTE) core network, and also be linkedover a Diameter Rx interface with a Proxy Call Session Control Function(P-CSCF) of an IMS.

When user equipment (UE), such as a mobile phone, attaches to atelecommunication network's core network, a gateway in the core networkthat is associated with the UE can establish a Gx session with a PCF.The PCF can store Gx binding information that associates the UE and thegateway with the established Gx session.

When a UE initiates a communication session, such as a session for aVoice over LTE (VoLTE) call, the UE can send a Session InitiationProtocol (SIP) message to the P-CSCF of the IMS. The P-CSCF can use anRx session to inform the PCF about the communication session for the UE,and the PCF can accordingly use its Gx binding information to identifywhich gateway is associated with the UE and find a corresponding Gxsession previously established with that gateway. The PCF can then usethat Gx session to provide the gateway with Policy and Charging Control(PCC) rules that define how the gateway should treat data for thatcommunication session, for instance by identifying a Quality of Service(QoS) or priority level associated with the communication session.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is set forth with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different figures indicates similaror identical items or features.

FIG. 1 depicts an example network environment in which user equipment(UE) can connect to a telecommunication network.

FIG. 2 depicts an example in which a core network is an LTE EPC, thegateway is an LTE P-GW, and the primary PCF is an LTE PCRF, while thebackup PCF is a 5G PCF.

FIG. 3 depicts an example in which the core network is a 5G corenetwork, the gateway is a 5G UPF, and the primary PCF is a 5G PCF, whilethe backup PCF is an LTE PCRF.

FIG. 4 depicts a sequence diagram showing messages sent between a UE andelements of a telecommunication network to prevent a new communicationsession from failing when a primary PCF is unreachable.

FIG. 5 depicts an example system architecture of a gateway.

FIG. 6 depicts an example system architecture of a P-CSCF of an IMS.

FIG. 7 depicts an example system architecture of a Policy ControlFunction (PCF).

FIG. 8 depicts a process by which a gateway can prevent a failedcommunication session by establishing a Gx session with a backup PCF ofa different network generation than the gateway.

FIG. 9 depicts a process by which a P-CSCF can prevent a failedcommunication session by contacting a backup PCF when a primary PCFcannot provide PCC rules for the communication session to a gateway.

DETAILED DESCRIPTION Introduction

A telecommunication network can include a core network, an IP MultimediaSubsystem (IMS), and Policy Control Functions (PCFs). The core networkcan process and route data packets, the IMS can set up and/or managecommunication sessions that use such data packets, and a PCF can providePolicy and Charging Control (PCC) rules defining how such data packetsshould be processed by the core network.

A PCF can be connected via Diameter protocol Gx interfaces to gatewaysof the core network. When a user equipment (UE) connects to a gateway,the gateway and the PCF can establish a Gx session over a Gx interfaceto exchange information about communications associated with that UE.The PCF can store Gx binding information about such established Gxsessions.

The PCF can also be connected via Diameter protocol Rx interfaces toelements of the IMS. For example, the PCF can be connected via an Rxinterface to a Proxy Call Session Control Function (P-CSCF) or otherapplication function (AF) of the IMS. When an P-CSCF receives a requestfrom a UE regarding a communication session, the P-CSCF can use the Rxinterface to request that the PCF provide the core network with PCCrules for that communication session. For example, if the UE requestsinitiation of a voice call, the P-CSCF can send a request over an Rxinterface to the PCF asking the PCF to provide the core network with PCCrules associated with setup of a dedicated bearer for voice call data.In this situation, the PCF can use its stored Gx binding information toidentify a Gx session previously established with the gateway that ishandling traffic for the UE. The PCF can accordingly send new or updatedPCC rules to that gateway over the previously established Gx session,and the gateway can apply the PCC rules.

However, if a PCF is offline or cannot be reached by the gateway and/orthe P-CSCF, new and existing communication sessions for a UE can fail.For example, when the PCF is offline entirely, the gateway would not beable to contact the PCF via an Gx interface, and the P-CSCF would alsonot be able to contact the PCF via an Rx interface. In this situation,the offline PCF would be unreachable by both the gateway and the P-CSCF,such that the P-CSCF could not use an Rx interface to request that thePCF provide PCC rules to the gateway for a new or existing communicationsession, and the gateway would not receive PCC rules for thecommunication session over a Gx interface such that the communicationsession fails.

As another example, if the PCF is online but a problem exists with theGx interface between the gateway and the PCF, the gateway may be unableto establish a Gx session with the PCF. In this situation, when no Gxsession is established between the gateway and the PCF for the UE, thegateway would not store Gx binding information associated with the UE.As such, even if the P-CSCF is able to use an Rx interface to requestthat the PCF provide the gateway with PCC rules for a new communicationsession, the PCF would return an error to the P-CSCF indicating that thePCF could not find a Gx session for the UE in its Gx bindinginformation. Accordingly, the new communication session would failbecause no Gx session was established that the PCF could use to providethe gateway with the PCC rules for the communication session. Forexample, a communication session for a requested voice call would failwhen the PCF is not able to provide a gateway with PCC rules for adedicated bearer for the voice call.

In some conventional systems, when a communication session fails due toan offline PCF or a broken Gx interface, setup of the communicationsession can be retried from the beginning via another PCF in the samepool of PCFs. However, this can cause delays and/or itself beunsuccessful. For example, if the gateway is linked to a pool of PCFsassigned to a particular geographical area where the UE is located, butall PCFs in that pool have gone offline due to errors introduced by asoftware update, a power outage, or any other issue, the gateway wouldbe unable to establish a Gx session with any of the PCFs in the pool andsetup of the communication session would again fail.

In some examples, circuit-switched fallback procedures may allow UEs toretry failed communication sessions on legacy circuit-switched networksthat do not involve an IMS or PCFs. For example, in an emergencysituation in which a UE was attempting to make a 911 call or otheremergency call to a public-safety answering point (PSAP), if theemergency call ultimately fails on a packet-switched network because ofissues caused by an offline PCF or a broken Gx interface as describedabove, the UE may be able to use circuit-switched fallback procedures toretry the emergency call on a legacy circuit-switched network. However,in many places a legacy circuit-switched network may not be available oraccessible by the UE, especially as network operators continue to focustheir efforts on newer packet-switched networks and decommission legacynetwork hardware. Accordingly, in some areas there may be no underlyingcircuit-switched coverage that the UE could use to attemptcircuit-switched fallback procedures. Even if a legacy circuit-switchednetwork is available, the legacy circuit-switched network may becomeoverloaded if numerous UEs begin using circuit-switched fallbackprocedures when their communication sessions fail due to offline PCFs orbroken Gx interfaces.

Accordingly, circuit-switched fallback procedures may not be a reliablebackup option when communication sessions fail due to an offline PCF ora broken Gx interface. Such a lack of a reliable backup circuit-switchedfallback option can be a problem for all types of communicationsessions, but be especially problematic for emergency calls and othercritical and time-sensitive types of communication sessions.

This disclosure describes systems and processes that allows Gx failuresassociated with a primary PCF to be detected early, before an attempt toset up a communication session fails entirely. When such failures aredetected in association with a primary PCF, a different type of PCFacting as a backup can be contacted over Gx and Rx interfaces. Forexample, the backup PCF can be associated with a different networkgeneration than the primary PCF, such that errors affecting Gx sessionsetup with the primary PCF may be less likely to occur with adifferent-generation backup PCF.

Communication sessions can thus be successfully set up though adifferent type of backup PCF, without setup of the communication sessionfailing overall and then needing to be retried in the same way or beattempted through alternative circuit-switched fallback methods. Earlydetection of Gx session failures can thus allow self-healing of atelecommunication network by setting up alternate Gx sessions instead ofletting communication sessions fail. Accordingly, the early Gx sessionfailure detection and self-healing processes described herein can makesetup of communication sessions through packet-switched networks morereliable, and thereby decrease the use of circuit-switched fallbackprocedures for emergency calls and other types of communications.

Example Environments

FIG. 1 depicts an example network environment in which user equipment(UE) 102 can connect to a telecommunication network to engage incommunication sessions for voice calls, video calls, messaging, datatransfers, or any other type of communication. A UE 102 can be anydevice that can wirelessly connect to the telecommunication network. Forexample, a UE 102 can be a mobile phone such as a smart phone or othercellular phone, a personal digital assistant (PDA), a personal computer(PC) such as a laptop, desktop, or workstation, a media player, atablet, a gaming device, a smart watch, a hotspot, or any other type ofcomputing or communication device.

The telecommunication network can include a core network that UEs 102can access through connections to base stations 104. Base stations 104can be access points that UEs 102 can wirelessly connect to in order toreach elements of the core network and other networks, as discussedbelow. The core network and/or base stations 104 can be compatible withone or more wireless access technologies, protocols, or standards. Forexample, wireless access technologies can include fifth generation (5G)technology, Long Term Evolution (LTE)/LTE Advanced technology, otherfourth generation (4G) technology, High-Speed Data Packet Access(HSDPA)/Evolved High-Speed Packet Access (HSPA+) technology, UniversalMobile Telecommunications System (UMTS) technology, Code DivisionMultiple Access (CDMA) technology, Global System for MobileCommunications (GSM) technology, WiMax® technology, WiFi® technology,and/or any other previous or future generation of wireless accesstechnology.

In some examples, base stations 104 can be part of a radio accessnetwork linked to the core network. For example, in an LTE network abase station 104 can be an evolved Node B (eNB), while in a 5G network abase station 104 can be referred to as a gNB. In other examples, a basestation 104 can be a Wi-Fi access point or other access point that canbe connected to the core network through the Internet or another type ofconnection.

The telecommunication network's core network can include multiplecomponents, including a management element 106 and gateways 108. Themanagement element 106 can be a control node that can assist in settingup and managing connections within the core network for UEs, for exampleby retrieving profiles of subscribers associated with the UEs 102 from aHome Subscriber Server (HSS) or other element, and/or by selectingparticular gateways 108 to handle connections for individual UEs 102.

Gateways 108 can be nodes that link the core network to base stations104, other networks such as the Internet or an IP Multimedia Subsystem(IMS) 110, and/or elements including a primary Policy Control Function(PCF) 112 and a backup PCF 114. Gateways 108 can set up default and/ordedicated bearers for UEs 102 within the core network, and route datapackets associated with UE 102 connections. Example architecture for agateway 108 is illustrated in greater detail in FIG. 5, and is describedin detail below with reference to that figure.

As will be described in more detail below, a gateway 108 can connect toa primary PCF 112 and/or a backup PCF 114 via Diameter Gx interfaces,such that the gateway 108 can exchange messages with the primary PCF 112and/or the backup PCF 114 over the Gx interfaces using the Diameterprotocol. For a particular UE 102, a gateway 108 and either the primaryPCF 112 or the backup PCF 114 can establish a Gx session, and theprimary PCF 112 or the backup PCF 114 can store Gx binding informationabout Gx session established with the gateway 108 for the UE 102. Insome examples, the gateway 108 can establish a passive Gx session withthe backup PCF 114 prior to attempting to set up Gx sessions with theprimary PCF 112, such that the gateway 108 can use the passive Gxsession to contact the backup PCF 114 and create Gx session binding fora UE 102 in situations where the gateway 108 cannot establish Gxsessions with the primary PCF 112.

The names and/or types of the management element 106 and gateways 108can vary depending on the type of the core network. For example, FIG. 2depicts an example in which the core network is an LTE Evolved PacketCore (EPC). In an LTE EPC, the management element 106 can be a MobilityManagement Entity (MME) 202, and the gateways 108 can include PacketData Network (PDN) Gateways (P-GWs) 204. A P-GW 204 can be a linkbetween the core network and the IMS 110, and also connect to theprimary PCF 112 and the backup PCF 114. Although only a P-GW 204 isshown as a gateway 108 in FIG. 2, the P-GW 204 may be linked to the MME202 and/or base station 104 though another type of gateway 108, aServing Gateway (S-GW). As another example, FIG. 3 depicts an example inwhich the core network is a 5G core network. In a 5G core network, themanagement element 106 can be a Session Management Function (SMF) 302,and the gateways 108 can include User Plane Functions (UPFs) 304.

The IMS 110 can include nodes and/or application functions (AFs) thatperform various operations to implement services with respect tocommunication sessions for a UE 102, such as services for voice calls,video calls, or any other type of communication. For example, the IMS110 can include a Proxy Call Session Control Function (P-CSCF) 116, alsoknown as a Session Border Controller (SBC) or Session Border Gateway(SBG), that serves as an entry point to the IMS 110. A P-CSCF 116 can becommunication with gateways 108 of the core network, such that theP-CSCF 116 can exchange Session Initiation Protocol (SIP) messages withindividual UEs 102 through gateways 108 associated with those UEs 102.For instance, a P-CSCF 116 can receive a SIP message from a UE 102requesting setup of a voice call (such as a Voice over LTE (VoLTE)call), a video call (such as a Video over LTE (ViLTE) call), or asession associated with any other type of communication or service. Asanother example, the IMS 110 can include an AF known as aa Web Real-TimeCommunication (WebRTC) Gateway (WRG), which can be an interface withinthe IMS 110 between web traffic and SIP messages, such that web trafficfrom a user originating from a web browser or other interface can betranslated into SIP messages for setting up or managing a communicationsession via the telecommunication network. The IMS 110 can also includeother Call Session Control Functions (CSCFs), such asInterrogating-CSCFs (I-CSCFs) and/or a Serving-CSCFs (S-CSCFs), and/orother application functions that can process, generate, and/or route SIPmessages, and/or otherwise manage elements of communication sessions.Example architecture for an IMS element, such as a P-CSCF 116, isillustrated in greater detail in FIG. 6, and is described in detailbelow with reference to that figure.

As will be discussed further below, a P-CSCF 116 or other AF of the IMS110 can also connect to a primary PCF 112 and/or a backup PCF 114 viaDiameter Rx interfaces, such that the P-CSCF 116 or other AF canexchange messages with the primary PCF 112 and/or the backup PCF 114over the Rx interfaces using the Diameter protocol. In some examples, aP-CSCF 116 or other AF can establish different Rx sessions with aprimary PCF 112 and a backup PCF 114 as peer Rx sessions.

As described above, a primary Policy Control Function (PCF) 112 and abackup PCF 114 can be linked to a gateway 108 of a core network throughDiameter Gx interfaces, and also be linked to a P-CSCF 116 or other AFof an IMS 110 through Diameter Rx interfaces. In some examples, aprimary PCF 112 can also be referred to as an active PCF, while a backupPCF 114 can also be referred to as a standby PCF or a passive PCF.Example architecture for a PCF is illustrated in greater detail in FIG.7, and is described in detail below with reference to that figure.

The primary PCF 112 and the backup PCF 114 can maintain Policy andCharging Control (PCC) policies corresponding to attributes ofcommunication session types, service types, subscriber or account types,a Quality of Service (QoS) level, and/or any other attribute. PCCpolicies can define PCC rules that can be applied to particularcommunication sessions for UEs 102 initiated via the IMS 110. Forexample, PCC rules can specify that data packets of a communicationsession should be given a certain priority level, be transmitted atleast at a minimum bitrate, be transmitted on certain bearers, and/or betreated in any other specified way. In some examples, PCC rules can alsodefine how a customer account is to be charged based on how data packetsare transmitted or treated during a communication session.

The primary PCF 112 and the backup PCF 114 can correspond to differentnetwork generations, such as different generations of wireless accesstechnologies, protocols, or standards. In some examples, the primary PCF112 may correspond to the same generation as the core network, while thebackup PCF 114 corresponds to an earlier or later generation than thecore network. The gateway 108 may be associated with the same generationas the core network overall, and be configured to use a same-generationPCF as the primary PCF 112. Accordingly, as will be described furtherbelow, the gateway 108 can be configured to first attempt to contact asame-generation PCF as a primary PCF 112. However, if the gateway 108cannot successfully reach a same-generation primary PCF 112 over a Gxinterface, the gateway 108 can be configured to contact adifferent-generation backup PCF 114 over a Gx interface. For example,the gateway 108 may have previously established a passive Gx sessionwith the backup PCF 114, such that the gateway 108 can use thealready-existing passive Gx session to contact the backup PCF 114 whenthe gateway 108 cannot set up a Gx session with the primary PCF 112.Although the primary PCF 112 and the backup PCF 114 can be associatedwith different network generations, both can store the same orsubstantially similar PCC rules for communication sessions, such thateither can send appropriate PCC rules to a gateway 108 of the same or adifferent network generation.

FIG. 2 depicts an example in which the core network is an LTE EPC, thegateway 108 is an LTE P-GW 204, and the primary PCF 112 is an LTE Policyand Charging Rules Function (PCRF) 206, while the backup PCF 114 is a 5GPCF 208. Accordingly, the 5G PCF 208 can serve as a backup PCF 114 eventhough the 5G PCF 208 is associated with a later network generation thanthe LTE EPC and its P-GWs 204. The 5G backup PCF 114 can thus assist insetting up a communication session for a UE connected to an LTE gateway108, regardless of whether or not the UE 102 itself is 5G-compatible.

FIG. 3 depicts another example in which the core network is a 5G corenetwork, the gateway 108 is a 5G UPF 304, and the primary PCF 112 is a5G PCF 208, while the backup PCF 114 is an LTE PCRF 206. Accordingly,the LTE PCRF 206 can serve as a backup PCF 114 even though the LTE PCRF206 is associated with an earlier network generation than the 5G corenetwork and its UPFs 304.

In some examples, a telecommunication network can operate differentgenerations of core networks concurrently, such that a PCF of aparticular generation can be used as both a primary PCF 112 for gateways108 of the same generation as well as a backup PCF 114 for gateways 108of different generations. For example, an LTE PCRF 206 can be consideredas a primary PCF 112 for LTE P-GWs 204, but the same LTE PCRF 206 can beconsidered as a backup PCF 114 for 5G UPFs 304. Accordingly, aparticular PCF may primarily handle connections from same-generationgateways 108, but be available to step in as a backup PCF 114 whenneeded to handle connections from different-generation gateways 108.

In some examples, the telecommunication network may have a pool ofprimary PCFs 112 and/or a pool of backup PCFs 114. For instance, an LTEnetwork can have a set of LTE PCRFs 206 that are used as a pool ofprimary PCFs 112 for a particular area, but also have access to a poolof 5G PCFs 208 that can serve as backup PCFs 114.

The primary PCF 112 and the backup PCF 114 can maintain Gx bindinginformation about Gx sessions that have been established between it andgateways 108 for UEs 102. When a primary PCF 112 or a backup PCF 114needs to send a message to a gateway 108 about a communication sessionfor a particular UE 102, such as when the primary PCF 112 or the backupPCF 114 receives information about a communication session from a P-CSCF116 over an Rx session and is configured to send new or updated PCCrules to a gateway 108 for the communication session, the primary PCF112 or the backup PCF 114 can use its Gx binding information to identifya previously established Gx session associated with that UE 102 and/orto identify the particular gateway 108 associated with that UE 102. Theprimary PCF 112 or the backup PCF 114 can then use that Gx bindinginformation to send the message, for instance a message including new orupdated PCC rules, to the gateway 108 over the established Gx session.

For example, in FIG. 2, the primary PCF 112 or the backup PCF 114 canreceive information about a communication session for a UE 102 from aP-CSCF 116 over an Rx interface, and in response use its Gx bindinginformation to identify a Gx session previously established with P-GW204 for the UE 102. The primary PCF 112 or the backup PCF 114 can thussend PCC rules for the UE's communication session to the P-GW 204 overthe identified Gx session, and the P-GW 204 can apply the PCC rules tothe communication session. For instance, the P-GW 204 can have a Policyand Charging Enforcement Function (PCEF) that analyses data packets,determines which communication session the data packets are associatedwith, and applies any applicable PCC rules to those data packets. Insome examples, if PCC rules are associated with a type of bearer thathas not yet been set up in the core network, such as a default bearer ordedicated bearer, receipt of the PCC rules at the P-GW 204 can cause theP-GW 204 to set up that type of bearer and then apply the PCC rules totraffic associated with that bearer.

Although a gateway 108 can attempt to establish a Gx session with aprimary PCF 112 associated with the same network generation as thegateway 108 as described above, in some examples the gateway 108 cannotestablish a Gx session with the primary PCF 112. For example, theprimary PCF 112 may be offline, or a problem may exist with the Gxinterface between the gateway 108 and the primary PCF 112, such that aGx session cannot be established between the gateway 108 and the primaryPCF 112. However, in this situation, the gateway 108 can follow policyrules that automatically trigger actions for the gateway 108 to contacta backup PCF 114 of a different network generation over a Gx interfacesuch that a GX binding is created at the backup PCF 114 between thegateway 108 and the backup PCF 114 for the UE 102. The gateway 108 canthus be network-aware, and take alternative action based on the policyrules to self-heal the telecommunication network by establishing a Gxsession binding with a backup PCF 114 when a Gx session with the primaryPCF 112 cannot be established.

For example, the gateway 108 may have previously created a passive Gxsession with the backup PCF 114 that it can use to contact the backupPCF 114 and create a Gx session binding for the UE 102 when the gatewaycannot establish a Gx session with the primary PCF 112. In someexamples, the gateway 108 can use an existing passive Gx session withthe backup PCF 114 to contact the backup PCF 114 about a communicationsession for a UE 102. Based on that contact over the passive Gx session,a new active Gx session for the UE 102 can be established between thegateway 108 and the backup PCF 114 and the backup PCF 114 can storecorresponding Gx binding information about the new active Gx session. Inother examples, a gateway's use of an existing passive Gx session tocontact a backup PCF 114 about a communication session for a UE 102 mayconvert the passive Gx session to an active Gx session between thegateway 108 and the backup PCF 114 for the UE 102, and the backup PCF114 can create or update associated Gx binding information. In stillother examples, if a passive Gx session with the backup PCF 114 does notalready exist, the gateway 108 can establish a new Gx session with thebackup PCF 114 for the UE 102, and the backup PCF 114 can create Gxbinding information about the new Gx session for the UE 102.

Because the backup PCF 114 may be associated with a different networkgeneration than the primary PCF 112, issues that may have affected theprimary PCF 112 and prevented establishment of a Gx session with theprimary PCF 112 may not have affected the backup PCF 114, and a Gxsession binding for the UE 102 can be established between the gateway108 and the backup PCF 114. For example, software issues that may havecaused one or more LTE PCRFs 206 to go offline may not have affected 5GPCFs 208. Accordingly, in the example of FIG. 2, an LTE P-GW 204 canestablish Gx session binding for a UE 102 with a 5G PCF 208 instead ofan LTE PCRF 206, and the 5G PCF 208 can store Gx binding informationabout the Gx session established between the LTE P-GW 204 and the 5G PCF208 for the UE 102.

Similarly, although a P-CSCF 116 or AF can attempt to send informationabout a UE's communication session to a primary PCF 112 over an Rxsession as described above, in some examples the P-CSCF 116 or AF cannotreach the primary PCF 112, or the primary PCF 112 cannot locate Gxbinding information associated with the UE 102. For example, a P-CSCF116 may be unable to contact the primary PCF 112 over an Rx session ifthe primary PCF 112 is offline or if there is a problem with the Rxinterface between the P-CSCF 116 and the primary PCF 112. As anotherexample, a P-CSCF 116 may be able to use an Rx session to successfullycontact a primary PCF 112 about a UE's communication session, but theprimary PCF 112 may be unable to locate Gx binding informationassociated with the UE 102 because there was a Gx interface failurebetween the gateway 108 and the primary PCF 112 such that no Gx sessionwas ever established with the primary PCF 112 in association with the UE102. In these situations, a P-CSCF 116 or AF can use a peer Rx sessionto instead contact the backup PCF 114 about the communication sessionfor the UE 102. As discussed above, the backup PCF 114 may haveestablished a Gx session with the gateway 108 associated with the UE 102and stored corresponding Gx binding information as discussed above. Thebackup PCF 114 can accordingly use its Gx binding information to findthe established Gx session and contact the gateway 108 about the UE'scommunication session, for example by sending new PCC rules to thegateway 108 over the Gx session.

In some examples, a P-CSCF 116 or other AF of the IMS 110 can determinewhich PCFs are the primary PCF 112 and the backup PCF 114 based on atype or configuration of the P-CSCF 116 or the AF, or the type ofservice associated with a requested communication session. For example,when a P-CSCF 116 is configured to assist with setup of VoLTE calls orSIP message received from a UE 102 requests setup of a VoLTE call, theP-CSCF 116 can consider an LTE PCRF 206 to be the primary PCF 112 and a5G PCF 208 to be the backup PCF 114. However, if the P-CSCF 116 isconfigured to assist with 5G-specific services or receives a SIP messageabout a 5G-specific service, the P-CSCF 116 can consider a 5G PCF 208 tobe the primary PCF 112 and an LTE PCRF 206 to be the backup PCF 114.

FIG. 4 depicts a sequence diagram showing messages sent between a UE 102and elements of a telecommunication network. The messages shown in FIG.4 can prevent a new communication session for a UE 102 from failing whena primary PCF 112 is unreachable due to Gx and/or Rx session issues byinstead setting up the communication session in part using Gx and Rxsessions with a different-generation backup PCF 114.

When a UE 102 connects to a base station 104, the UE 102 can send anattach request 402 through the base station 104 to the core network'smanagement element 106, such as an MME 202 or SMF 302. In some examples,the attach request 402 can specify an Access Point Name (APN) of a PDNthat the UE 102 has requested to be connected to, for instance the IMS110. In other examples, the management element 106 can look up a profileassociated with the UE 102, for example by retrieving a subscriberprofile from an HSS, and find a default APN listed in the profile forthe UE, such as the IMS 110.

The management element 106 can select one or more gateways 108 of thecore network for the UE 102, for instance by selecting an S-GW and aP-GW 204 for the UE 102 in an LTE EPC or by selecting a UPF 304 for theUE 102 in a 5G core network. The management element 106 can then send acreate session request 404 to a selected gateway, such as a P-GW 204 orUPF 304. The create session request 404 can include information from theattach request 402 and/or the profile, such as an international mobilesubscriber identity (IMSI) or the APN.

Based on receipt of the create session request 404, the gateway 108 canattempt to send a credit control request (CCR) 406 over a Gx interfaceto a primary PCF 112. The CCR 406 can identify attributes associatedwith the UE 102 or a corresponding user profile, such as the IMSI andthe APN.

However, a Gx session error 408 can occur in response to the CCR 406. AGx session error 408 can be an explicit error message returned to thegateway 108 from the primary PCF 112, or be a timeout error when thegateway 108 does not receive a response to the CCR 406 from the primaryPCF 112 within a predetermined period of time. For example, the primaryPCF 112 may return an explicit Gx session error 408 message indicatingthat the primary PCF 112 is overloaded or is experiencing problems thatprevent it from processing the CCR 406. As another example, if theprimary PCF 112 is offline or the Gx interface between the gateway 108and the primary PCF 112 is broken for any reason such that the CCR 406cannot reach the primary PCF 112 over the Gx interface, the primary PCF112 may not respond to the CCR 406 within a predetermined period oftime. Accordingly, the gateway 108 can wait for a response to the CCR406, but determine that a timeout error has occurred when no response tothe CCR 406 is received from the primary PCF 112 within thepredetermined period of time.

In conventional systems, a Gx session error 408 may lead to a UE'sattachment to the telecommunication network failing immediately, or theUE 102 attaching to the telecommunication network when no Gx session hasbeen established between a gateway 108 and a PCF. Accordingly, in suchconventional systems new communication sessions may fail becausecorresponding PCC rules cannot be provided by the PCF to the gateway 108over the non-established Gx session.

However, as described herein, when a Gx session error 408 occurs, herethe gateway 108 can use policy rules to determine a next action that mayprevent failure of attempted communication sessions, such as sending theCCR 406 to a backup PCF 112 over a Gx interface. In some examples, thegateway 108 and the backup PCF 114 may have previously established apassive Gx session for use in cases when the gateway 108 cannotestablish a Gx session with the primary PCF 112, and the CCR 406 can besent to the backup PCF 114 over the previously established passive Gxsession. In other examples, the gateway 108 can establish a new Gxsession with the backup PCF 114 after a Gx session error 408 occurs, andthe CCR 406 can be sent to the backup PCF 114 over the new Gx session.The gateway's policy rules can therefore allow the telecommunicationnetwork to self-heal and prevent communication session failures when Gxsession errors 408 are detected.

For example, when the gateway 108 sends a CCR 406A to the primary PCF112 but a Gx session error 408 occurs, the gateway's policy rules cantrigger the gateway 108 to send a CCR 406B to the backup PCF 114 over aGx interface. CCR 406B can be substantially similar to CCR 406A, andalso include an IMSI, APN, and/or other information that had beenincluded in CCR 406A. As noted above, the backup PCF 114 can beassociated with a different network generation than the primary PCF 112and/or the gateway 108. For example, when the gateway 108 is an LTE P-GW204 and the primary PCF 112 is an LTE PCRF 206, but the LTE PCRF 206does not respond to a CCR 406A from the LTE P-GW 204, the LTE P-GW 204can send a CCR 406B to a 5G PCF 208 acting as a backup PCF 114. Asanother example, when the gateway 108 is a 5G UPF 304 and the primaryPCF 112 is a 5G PCF 208, but the 5G PCF 208 does not respond to a CCR406A from the 5G UPF 304, the 5G UPF 304 can send a CCR 406B to an LTEPCRF 206 acting as a backup PCF 114.

In some examples, the gateway 108 can track statistics about responsesto CCRs 406 sent to the primary PCF 112, such as a failure rateindicating how frequently Gx session errors 408 occur relative to CCRs406 that are sent. In these examples, the policy rules may indicate thatif the failure rate is below a threshold value, the gateway 108 should,upon a Gx session error 408, re-try sending a CCR 406 to the primary PCF112 or another primary PCF 112 in a pool of primary PCFs 112. However,the policy rules may also indicate that if the failure rate is at orabove the threshold value, the gateway 108 should, upon a Gx sessionerror 408, instead send the CCR 406 to a backup PCF 114 of a differentnetwork generation rather than the primary PCF 112. In other examples,the policy rules may indicate that the gateway 108 should immediatelysend the CCR 406 to a backup PCF 114 upon a single occurrence of a Gxsession error 408, send the CCR 406 to a backup PCF 114 when a count offailed CCRs 406 sent to the primary PCF 112 exceeds a threshold, or uponthe occurrence of any other criteria or condition.

In some examples, comparing a failure rate or other statisticsassociated with sent CCRs 406 and occurrences of Gx session errors 408can cause a gateway 108 to predict that a primary PCF 112 is unreliableor is likely to fail even if the primary PCF 112 is not yet entirelyoffline or inaccessible. For example, when a primary PCF 112 isoverloaded, the primary PCF 112 may still be able to respond normally tosome CCRs 406. However, when a failure rate tracked by the gateway 108shows that timeout errors have been occurring in association with theprimary PCF 112 more frequently than a predefined threshold, even thoughthe primary PCF 112 may have responded to some CCRs 406 in a timelymanner, the gateway 108 can use policy rules to determine that theprimary PCF 112 is unreliable or may be near failure. Accordingly, thepolicy rules can, in response to the Gx session error 408, automaticallytrigger the gateway 108 to switch to a backup PCF 114 and send the CCR406 to the backup PCF 114.

After the gateway 108 sends a CCR 406 to the backup PCF 114 over a Gxinterface, the backup PCF 114 can respond by returning a credit controlanswer (CCA) 410 to the gateway 108 over the Gx interface. The CCA 410can indicate that a Gx session binding has been established between thegateway 108 and the backup PCF 114 with respect to the UE 102. Thebackup PCF 114 can also store Gx binding information associated with theestablished Gx session, such that the backup PCF 114 can later use theGx binding information to identify the gateway 108 and the Gx sessionassociated with the UE 102. For example, the Gx binding information canidentify attributes of the Gx session, such as identifiers for the UE102, the gateway 108, an APN, such as an APN for the IMS 110, and/or anyother attribute.

When the gateway 108 receives a CCA 410 from the backup PCF 114, thegateway 108 can send a create session response 412 to the managementelement 106, which can in turn send an attach acceptance 414 to the UE102. At this point, the UE 102 can be attached to the core network and adata session or default bearer for the UE 102 can exist within the corenetwork, despite the occurrence of the Gx session error 408 associatedwith the primary PCF 112. Similarly, despite the occurrence of the Gxsession error 408 associated with the primary PCF 112, Gx sessionbinding can have been established for the UE 102 between the gateway 108and the backup PCF 114. Accordingly, as will be discussed below, thebackup PCF 114 can use the established Gx session binding to provide thegateway 108 with PCC rules for a communication session, therebypreventing failure of the communication session due to non-establishedGx session binding.

After the UE 102 has attached to the core network, the UE 102 can send aSession Initiation Protocol (SIP) message 416 about a communicationsession to the P-CSCF 116. For example, the UE 102 can send the P-CSCF116 a SIP REGISTER message or a SIP INVITE message to initiate a voicecall. In some examples, the UE 102 may have been given an IP address forthe P-CSCF 116 during attachment to the core network such that the UE102 can send SIP messages to the P-CSCF 116.

When the P-CSCF 116 receives a SIP message from a UE 102, the P-CSCF 116can attempt to set up resources in the core network for a communicationsession for the UE 102. This attempt can include asking a PCF to providePCC rules applicable to the communication session to a gateway 108associated with the UE 102. However, although the gateway 108 may havedetermined based on the Gx session error 408 that the primary PCF 112 isoffline or cannot be contacted via an Gx interface as discussed above,there may be no message format defined that would allow the gateway 108to inform the P-CSCF 116 that the primary PCF 112 may be offline or thatthe gateway 108 could not establish a Gx session with the primary PCF112 and established a Gx session with the backup PCF 114 instead.

Accordingly, the P-CSCF 116 can first attempt to contact the primary PCF112 about the UE's communication session by attempting to send theprimary PCF 112 an Authorize/Authenticate Request (AAR) 418 message overan Rx interface. The AAR 418 can include an identifier for the UE 102,an identifier for the type of communication session, and/or any otherinformation, and request that the primary PCF 112 send PCC rulesapplicable to the communication session to a gateway 108 associated withthe UE 102. For example, when the P-CSCF 116 received a SIP message 416from a UE 102 requesting initiation of a VoLTE call, the P-CSCF 116 canidentify an LTE PCRF 206 as the primary PCF 112 and attempt to send anAAR 418 to the LTE PCRF 206. The P-CSCF 116 can attempt to send the AAR418 to the primary PCF 112 to request that the primary PCF 112 use Gxbinding information stored at the primary PCF to identify a P-GW 204associated the UE 102 and use a previously established Gx session toprovide the P-GW 204 with PCC rules for a dedicated bearer for the VoLTEcall. However, as discussed above, the primary PCF 112 may not have suchGx binding information because a Gx session error 408 occurred and no Gxsession was established between the gateway 108 and the primary PCF 112for the UE 102.

Accordingly, a Gx binding unavailable error 420 can occur in response tothe AAR 418 sent by the P-CSCF 116 to the primary PCF 112. In someexamples, a Gx binding unavailable error 420 can be an explicit errormessage returned to the P-CSCF 116 from the primary PCF 112. Forexample, the primary PCF's Gx binding information may not includeinformation about a Gx session between the primary PCF 112 and thegateway 108 for the UE 102 when the Gx interface between the primary PCF112 and the gateway 108 was broken and a Gx session error 408 occurred.Accordingly, the primary PCF 112 would not be able to find informationabout an established Gx session with a gateway 108 for the UE 102 in itsGx binding information in response to the P-CSCF's AAR 418. The primaryPCF 112 can therefore return a Gx binding unavailable error 420 to theP-CSCF 116 as an explicit message over the Rx interface indicating thatthe primary PCF 112 has no Gx binding information about the UE 102, forexample as a Diameter 5065 “IP-CAN_SESSION_NOT_AVAILABLE” message. Inother examples, the primary PCF 112 may return another type of Gxbinding unavailable error 420 message indicating that the primary PCF112 is overloaded or is experiencing problems that prevent it fromprocessing the AAR 418.

In other examples, if the primary PCF 112 is offline or the Rx interfacebetween the P-CSCF 116 and the primary PCF 112 is broken for any reasonsuch that the AAR 418 cannot reach the primary PCF 112, the primary PCF112 may not respond to the AAR 418 within a predetermined period oftime. Accordingly, the P-CSCF 116 can wait for a response to the AAR418, but determine that a Gx binding unavailable error 420 has occurredwhen no response to the AAR 418 is received from the primary PCF 112within the predetermined period of time.

In conventional systems, a Gx binding unavailable error 420 may lead tothe failure of a new communication session. For example, when a Gxbinding unavailable error 420 occurs because a PCF cannot find Gxbinding information associated with a UE 102, the PCF cannot use anestablished Gx session to send PCC rules to gateway 108 about how totreat data of that communication session, and setup of the communicationsession can accordingly fail. However, as described herein, when a Gxbinding unavailable error 420 occurs, here the P-CSCF 116 can use policyrules to determine a next action that may prevent failure of attemptedcommunication sessions.

For example, when the P-CSCF 116 sends an AAR 418A to the primary PCF112 but a Gx binding unavailable error 420 occurs, the P-CSCF 116 cansend an AAR 418B to the backup PCF 114 over an Rx interface based onpolicy rules. For example, the P-CSCF 116 can have previouslyestablished peer Rx sessions with multiple PCFs, including the primaryPCF 112 and backup PCF 114. Accordingly, when a Gx binding unavailableerror 420 occurs with respect to a primary PCF 112, the P-CSCF's policyrules can indicate that the P-CSCF 116 should use a peer Rx session thathas already been established with a backup PCF 114 to send the AAR 418to the backup PCF 114.

When the backup PCF 114 does have Gx binding information about the UE102 as discussed above, the backup PCF 114 can return anAuthorize/Authenticate Answer (AAA) 422 to the P-CSCF 116 over the peerRx session to confirm that the Gx binding information has been found.The backup PCF 114 can also perform any actions requested by the P-CSCF116 in the AAR 418 once it has found the Gx binding information andidentified an existing Gx session with a gateway 108 for the UE 102. Forexample, the backup PCF 114 can provide new or modified PCC rules for aVoLTE call or any other type of communication session.

Accordingly, although the primary PCF 112 would have been unable to findGx binding information for a UE 102 in response to an AAR 418, forexample because it was offline or a Gx session for the UE 102 was neverestablished with the primary PCF 112, the UE's communication session canstill be set up or modified by the backup PCF 114 as requested by theP-CSCF 116 despite the occurrence of the Gx binding unavailable error420.

As described above, in conventional systems setup of communicationsession for a UE 102 may fail entirely due to a Gx session error 408and/or a Gx binding unavailable error 420. Accordingly, in suchconventional systems a UE 102 would either need to retry the failedcommunication session in the same way or attempt circuit-switchedfallback procedures. Both of these actions in conventional systems mayintroduce delay, or fail themselves. However, such delays andcommunication session setup failures can be prevented as describedherein by having a gateway 108 contact a backup PCF 114 upon a Gxsession error 408 and by having a P-CSCF 116 contact the backup PCF 114upon a Gx binding unavailable error 420.

Example Architecture

FIG. 5 depicts an example system architecture of a gateway 108. Asdescribed above, the gateway 108 can be an LTE P-GW 204, a 5G UPF 304,or any other type of gateway 108 that can connect a core network to aprimary PCF 112 and/or a backup PCF 114 via Diameter Gx interfaces.

The gateway 108 can be, or run on, a computing device that has a systemmemory 502. The system memory 502 can store data for the gateway 108,including policy rules 504 and/or other modules and data 506. Thecomputing device of the gateway 108 can also include processor(s) 508,removable storage 510, non-removable storage 512, input device(s) 514,output device(s) 516, and/or communication connections 518 forcommunicating with other network elements 520.

In various examples, system memory 502 can be volatile (such as RAM),non-volatile (such as ROM, flash memory, etc.), or some combination ofthe two. Example system memory 502 can include one or more of RAM, ROM,EEPROM, a Flash Memory, a hard drive, a memory card, an optical storage,a magnetic cassette, a magnetic tape, a magnetic disk storage or anothermagnetic storage devices, or any other medium.

The gateway's policy rules 504 can indicate when the gateway 108 shouldsend a CCR 406 to a backup PCF 114 instead of a primary PCF 112. Forexample, the gateway 108 can track statistics associated with Gx sessionerrors 408, such as a failure rate or failure count, and the policyrules 504 can indicate that the gateway 108 should send a CCR 406 to abackup PCF 114 instead of a primary PCF 112 when a Gx session error 408occurs and the statistics meet a threshold value. The policy rules 504can thus make the gateway 108 network-aware and let thetelecommunication network self-heal when Gx session errors 408 occur.For example, the gateway 108 can recognize when a Gx session has notbeen established with a primary PCF 112, which may lead to setup of acommunication session failing, and instead take alternative action tocontact a backup PCF 114 via a Gx session. In some examples, the policyrules 504 can identify which PCFs are considered the primary PCF 112 andthe backup PCF 114 for the gateway 108.

The other modules and data 506 can be utilized by the gateway 108 toperform or enable performing any action taken by the gateway 108. Theother modules and data 506 can include a platform and applications, anddata utilized by the platform and applications.

In some examples, the processor(s) 508 can be a central processing unit(CPU), a graphics processing unit (GPU), both CPU and GPU, or otherprocessing unit or component known in the art.

The computing device of the gateway 108 can also include additional datastorage devices (removable and/or non-removable) such as, for example,magnetic disks, optical disks, or tape. Such additional storage isillustrated in FIG. 5 by removable storage 510 and non-removable storage512. Computer storage media may include volatile and nonvolatile,removable and non-removable media implemented in any method ortechnology for storage of information, such as computer readableinstructions, data structures, program modules, or other data. Systemmemory 502, removable storage 510 and non-removable storage 512 are allexamples of computer-readable storage media. Computer-readable storagemedia include, but are not limited to, RAM, ROM, EEPROM, flash memory orother memory technology, CD-ROM, digital versatile discs (DVD) or otheroptical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, or any other medium which canbe used to store the desired information and which can be accessed bythe gateway 108. Any such computer-readable storage media can be part ofthe gateway 108. In various examples, any or all of system memory 502,removable storage 510, and non-removable storage 512, store programminginstructions which, when executed, implement some or all of theherein-described operations of the gateway 108.

In some examples, the computing device of the gateway 108 can also haveinput device(s) 514, such as a keyboard, a mouse, a touch-sensitivedisplay, voice input device, etc., and/or output device(s) 516 such as adisplay, speakers, a printer, etc. These devices are well known in theart and need not be discussed at length here.

The computing device of the gateway 108 can also contain communicationconnections 518 that allow the gateway 108 to communicate with othernetwork elements 520 such as UEs 102, base stations 104, other gateways108, other elements of the core network, elements of the IMS 110,primary PCFs 112, backup PCFs 114, and/or any other elements of thetelecommunication network. For example, the communication connections518 can be associated with Diameter Gx interfaces that allow Gx sessionsto be established between the gateway 108 and a primary PCF 112 or abackup PCF 114.

FIG. 6 depicts an example system architecture of a P-CSCF 116 of an IMS110. In some examples, other application functions of an IMS 110 thatcan connect to a primary PCF 112 and/or a backup PCF 114 via Diameter Rxinterfaces can also have the example system architecture shown in FIG.6.

The P-CSCF 116 can be, or run on, a computing device that has a systemmemory 602. The system memory 602 can store data for the P-CSCF 116,including policy rules 604 and/or other modules and data 606. Thecomputing device of the P-CSCF 116 can also include processor(s) 608,removable storage 610, non-removable storage 612, input device(s) 614,output device(s) 616, and/or communication connections 618 forcommunicating with other network elements 620.

In various examples, system memory 602 can be volatile (such as RAM),non-volatile (such as ROM, flash memory, etc.), or some combination ofthe two. Example system memory 602 can include one or more of RAM, ROM,EEPROM, a Flash Memory, a hard drive, a memory card, an optical storage,a magnetic cassette, a magnetic tape, a magnetic disk storage or anothermagnetic storage devices, or any other medium.

The P-CSCF's policy rules 604 can indicate when the P-CSCF 116 shouldsend an AAR 418 to a backup PCF 114 instead of a primary PCF 112. Forexample, the policy rules 604 can indicate that the P-CSCF 116 shouldsend an AAR 418 to a backup PCF 114 instead of a primary PCF 112 when aGx binding unavailable error 420 occurs. The policy rules 604 can thusmake the P-CSCF 116 network-aware, such that the P-CSCF 116 canrecognize when a Gx binding unavailable error 420 would cause setup of acommunication session to fail, and instead take alternative action toset up the communication session via a peer Rx session with the backupPCF 114. In some examples, the policy rules 604 can identify which PCFsare considered the primary PCF 112 and the backup PCF 114 for the P-CSCF116.

The other modules and data 606 can be utilized by the P-CSCF 116 toperform or enable performing any action taken by the P-CSCF 116. Theother modules and data 606 can include a platform and applications, anddata utilized by the platform and applications.

In some examples, the processor(s) 608 can be a central processing unit(CPU), a graphics processing unit (GPU), both CPU and GPU, or otherprocessing unit or component known in the art.

The computing device of the P-CSCF 116 can also include additional datastorage devices (removable and/or non-removable) such as, for example,magnetic disks, optical disks, or tape. Such additional storage isillustrated in FIG. 6 by removable storage 610 and non-removable storage612. Computer storage media may include volatile and nonvolatile,removable and non-removable media implemented in any method ortechnology for storage of information, such as computer readableinstructions, data structures, program modules, or other data. Systemmemory 602, removable storage 610 and non-removable storage 612 are allexamples of computer-readable storage media. Computer-readable storagemedia include, but are not limited to, RAM, ROM, EEPROM, flash memory orother memory technology, CD-ROM, digital versatile discs (DVD) or otheroptical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, or any other medium which canbe used to store the desired information and which can be accessed bythe P-CSCF 116. Any such computer-readable storage media can be part ofthe P-CSCF 116. In various examples, any or all of system memory 602,removable storage 610, and non-removable storage 612, store programminginstructions which, when executed, implement some or all of theherein-described operations of the P-CSCF 116.

In some examples, the computing device of the P-CSCF 116 can also haveinput device(s) 614, such as a keyboard, a mouse, a touch-sensitivedisplay, voice input device, etc., and/or output device(s) 616 such as adisplay, speakers, a printer, etc. These devices are well known in theart and need not be discussed at length here.

The computing device of the P-CSCF 116 can also contain communicationconnections 618 that allow the P-CSCF 116 to communicate with othernetwork elements 620 such as UEs 102 via elements of the core network,other elements of the IMS 110, primary PCFs 112, backup PCFs 114, and/orany other elements of the telecommunication network. For example, thecommunication connections 618 can be used to send or receive SIPmessages or be associated with Diameter Rx interfaces that allow peer Rxsessions to be established between the P-CSCF 116 and a primary PCF 112and/or a backup PCF 114.

FIG. 7 depicts an example system architecture of a PCF 700. The PCF 700can be either a primary PCF 112 or a backup PCF 114. A PCF 700 can be anLTE PCRF 206, a 5G PCF 208, or any other type of PCF 700 that canconnect to gateways 108 via Diameter Gx interfaces and to P-CSCFs 116 orother IMS application functions via Diameter Rx interfaces.

The PCF 700 can be, or run on, a computing device that has a systemmemory 702. The system memory 702 can store data for the PCF 700,including Gx binding information 704, PCC rules 706, and/or othermodules and data 708. The computing device of the PCF 700 can alsoinclude processor(s) 710, removable storage 712, non-removable storage714, input device(s) 716, output device(s) 718, and/or communicationconnections 720 for communicating with other network elements 722.

In various examples, system memory 702 can be volatile (such as RAM),non-volatile (such as ROM, flash memory, etc.), or some combination ofthe two. Example system memory 702 can include one or more of RAM, ROM,EEPROM, a Flash Memory, a hard drive, a memory card, an optical storage,a magnetic cassette, a magnetic tape, a magnetic disk storage or anothermagnetic storage devices, or any other medium.

The PCF's Gx binding information 704 can include information about Gxsessions that have been set up for UEs 102 between the PCF 700 andgateways 108. When the PCF 700 receives an AAR 418 from a P-CSCF 116 oran AF of the IMS 110 about a communication session for a UE, the PCF 700can use the Gx binding information 704 to identify a previouslyestablished Gx session with a gateway 108 for that UE 102. The PCF 700can then use the previously established Gx session to provide thegateway 108 with PCC rules 706 applicable to the communication session.

The PCF's PCC rules can be rules that can be applied to communicationsessions for UEs 102 by gateways 108 or other network elements. The PCCrules may correspond to attributes of communication session types,service types, subscriber or account types, a Quality of Service (QoS)level, and/or any other attribute. For example, PCC rules can specifythat data packets of a communication session should be given a certainpriority level, be transmitted at least at a minimum bitrate, betransmitted on certain bearers, and/or be treated in any other specifiedway. In some examples, PCC rules can also define how a customer accountis to be charged based on how data packets are transmitted or treatedduring a communication session.

The other modules and data 708 can be utilized by the PCF 700 to performor enable performing any action taken by the PCF 700. The other modulesand data 708 can include a platform and applications, and data utilizedby the platform and applications.

In some examples, the processor(s) 710 can be a central processing unit(CPU), a graphics processing unit (GPU), both CPU and GPU, or otherprocessing unit or component known in the art.

The computing device of the PCF 700 can also include additional datastorage devices (removable and/or non-removable) such as, for example,magnetic disks, optical disks, or tape. Such additional storage isillustrated in FIG. 7 by removable storage 712 and non-removable storage714. Computer storage media may include volatile and nonvolatile,removable and non-removable media implemented in any method ortechnology for storage of information, such as computer readableinstructions, data structures, program modules, or other data. Systemmemory 702, removable storage 712 and non-removable storage 714 are allexamples of computer-readable storage media. Computer-readable storagemedia include, but are not limited to, RAM, ROM, EEPROM, flash memory orother memory technology, CD-ROM, digital versatile discs (DVD) or otheroptical storage, magnetic cassettes, magnetic tape, magnetic diskstorage or other magnetic storage devices, or any other medium which canbe used to store the desired information and which can be accessed bythe PCF 700. Any such computer-readable storage media can be part of thePCF 700. In various examples, any or all of system memory 702, removablestorage 712, and non-removable storage 714, store programminginstructions which, when executed, implement some or all of theherein-described operations of the PCF 700.

In some examples, the computing device of the PCF 700 can also haveinput device(s) 716, such as a keyboard, a mouse, a touch-sensitivedisplay, voice input device, etc., and/or output device(s) 718 such as adisplay, speakers, a printer, etc. These devices are well known in theart and need not be discussed at length here.

The computing device of the PCF 700 can also contain communicationconnections 720 that allow the PCF 700 to communicate with other networkelements 722 such as gateways 108 or elements of the IMS 110. Forexample, the communication connections 720 can be associated withDiameter Gx interfaces that allow Gx sessions to be established betweenthe PCF 700 and gateways 108, as well as Diameter Rx interfaces thatallow Rx sessions to be established between the PCF 700 and P-CSCFs 116or other IMS application functions.

Example Operations

FIG. 8 depicts a process by which a gateway 108 can prevent a failedcommunication session by establishing a Gx session with a backup PCF 114of a different network generation than the gateway 108.

At block 802, the gateway 108 can attempt to send a CCR 406 to a primaryPCF 112 over a Gx interface. In some examples, the gateway 108 may havereceived a create session request 404 from a management element 106 aspart of a network attach process for a UE 102, and the gateway 108 canrespond by attempting to send the CCR 406 to the primary PCF 112. Insome examples, the primary PCF 112 and the gateway 108 can be associatedwith the same network generation.

At block 804, the gateway 108 can determine that a Gx session error 408has occurred. In some examples, if the primary PCF 112 does not respondto the gateway's CCR 406 within a predetermined period of time, thegateway 108 can determine based on the lack of a response that a Gxsession error 408 has occurred. In other examples, the primary PCF 112can return an error message or other response indicating that theprimary PCF 112 cannot handle the CCR 406, and the gateway 108 candetermine that a Gx session error 408 has occurred based on the primaryPCF's response.

At block 806, the gateway 108 can update Gx session error statisticsassociated with the primary PCF 112 based on the occurrence of the Gxsession error 408. For example, over a period of time the gateway 108can track a failure rate indicating how frequently Gx session errors 408occur relative to CCRs 406 that have been sent to a primary PCF 112, ormaintain a count of a number of times Gx session errors 408 haveoccurred with respect to the primary PCF 112.

At block 808, the gateway 108 can use policy rules to determine if abackup PCF 114 should be used. For example, if Gx session errorstatistics indicate that a failure rate associated with CCRs 406 sent tothe primary PCF 112 is below a threshold value, the policy rules mayindicate that the gateway 108 should return to block 802 and re-trysending the CCR 406 to the primary PCF 112. However, if Gx session errorstatistics indicate that the failure rate associated with CCRs 406 sentto the primary PCF 112 is at or above a threshold value, the policyrules may indicate that the gateway 108 should instead send the CCR 406to a backup PCF 114 associated with a different network generation thanthe gateway 108. In some examples, block 806 can be absent, and thepolicy rules may indicate at block 808 that a CCR 406 should beimmediately sent to a backup PCF 114 when a single Gx session error 408occurs in association with a CCR 406 sent to the primary PCF 112 atblocks 802 and 804.

At block 810, the gateway 108 can send the CCR 406 to the backup PCF 114over a Gx interface. For examples, the gateway 108 can send the CCR 406to the backup PCF 114 by establishing and using a new Gx session withthe backup PCF 114, or by using a passive Gx session that was previouslyestablished with the backup PCF 114. In some examples, the backup PCF114 can be associated with a different network generation than thegateway 108 and the primary PCF 112, such that issues preventingestablishment of a Gx session with the primary PCF 112 may be lesslikely to impact a Gx session with the different-generation backup PCF114.

At block 812, the gateway 108 can receive a CCA 410 over the Gxinterface from the backup PCF 114. The CCA 410 can indicate that a Gxsession binding has been established between the gateway 108 and thebackup PCF 114 with respect to the UE 102, such that the backup PCF 114can later use the Gx binding information to identify the gateway 108 andthe Gx session associated with the UE 102. In some examples, the gateway108 can respond to the CCA 410 by sending a create session response 412back to the management element 106, such that the network attach processfor the UE 102 can be completed.

FIG. 9 depicts a process by which a P-CSCF 116 can prevent a failedcommunication session by contacting a backup PCF 114 when a primary PCF112 cannot provide PCC rules for the communication session to a gateway108.

At block 902, the P-CSCF 116 can establish peer Rx sessions with aprimary PCF 112 and a backup PCF 114. While in some examples, the P-CSCF116 can identify which peer Rx sessions are associated with the primaryPCF 112 and the backup PCF 114, in other examples the P-CSCF 116 canestablish peer Rx sessions with PCFs of different network generationssuch that either generation of PCF can serve as a primary PCF 112 or abackup PCF 114 depending on the situation.

At block 904, the P-CSCF 116 can attempt to send an AAR 418 to a primaryPCF 112 over an Rx session. In some examples, the P-CSCF 116 may havereceived a SIP message from a UE 102 regarding a new communicationsession, and the P-CSCF 116 can respond by attempting to send the AAR418 to a primary PCF 112. The AAR 418 can request that PCC rulesassociated with the new communication session be sent to a gateway 108associated with the UE 102.

As noted above, in some examples the P-CSCF 116 may have pre-identifiedwhich of the PCFs it has established peer Rx sessions with is theprimary PCF 112 and which is the backup PCF 114. For example, if theP-CSCF 116 is specifically associated with LTE services, then the P-CSCF116 can identify an LTE PCRF 206 as the primary PCF 112 and a 5G PCF 208as the backup PCF 114, and send the AAR 418 to the LTE PCRF 206 at block904. In other examples, the P-CSCF 116 may determine which of the PCFsit has established peer Rx sessions with is the primary PCF 112 andwhich is the backup PCF 114 from the type of the communication sessionrequested in the SIP message. For example, if the P-CSCF 116 isconfigured to manage services associated with different networkgenerations but the SIP message is specifically associated with a VoLTEcall, the P-CSCF 116 can determine that the LTE PCRF 206 is the primaryPCF 112 and send the AAR 418 to the LTE PCRF 206 at block 904.

At block 906, the P-CSCF 116 can determine that a Gx binding unavailableerror 420 has occurred. In some examples, if the primary PCF 112 doesnot respond to the P-CSCF's AAR 418 within a predetermined period oftime, the P-CSCF 116 can determine based on the lack of a response thata Gx binding unavailable error 420 has occurred. In other examples, theprimary PCF 112 can return a Diameter 5065“IP-CAN_SESSION_NOT_AVAILABLE” message or other explicit messageindicating that the primary PCF 112 cannot locate Gx binding informationassociated with the UE 102 or otherwise cannot process the AAR 418.

At block 908, the P-CSCF 116 can send the AAR 418 to the backup PCF 114over the previously established peer Rx interface. As noted above, insome examples the backup PCF 114 can be associated with a differentnetwork generation than the primary PCF 112, such that issues preventingestablishment of a Gx session between a gateway 108 and a primary PCF112 may have been less likely to impact establishment of a Gx sessionbetween the gateway 108 and the different-generation backup PCF 114.Accordingly, in situations in which the primary PCF 112 was offline orwas inaccessible to the gateway 108 over a Gx interface, the gateway 108can have established a Gx session for the UE 102 with the backup PCF 114instead. Accordingly, the backup PCF 114 can have Gx binding informationabout the Gx session with the gateway 108 for the UE 102.

At block 910, the P-CSCF 116 can receive an AAA 422 from the backup PCF114 over the peer Rx interface. The AAA 422 can confirm that the backupPCF 114 found Gx binding information for the UE 102 and will perform anyactions requested by the P-CSCF 116 in the AAR 418, such as providingthe gateway 108 with new or modified PCC rules for the communicationsession requested in the SIP message.

CONCLUSION

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter is not necessarily limited to the specificfeatures or acts described above. Rather, the specific features and actsdescribed above are disclosed as example embodiments.

1. A method comprising: sending, by a gateway of a telecommunicationnetwork, a Credit Control Request (CCR) associated with a user equipment(UE) to a primary Policy Control Function (PCF) over a first Gxinterface; detecting, by the gateway, a Gx session error associated withthe primary PCF indicating that a Gx session has not been establishedbetween the gateway and the primary PCF; in response to detecting the Gxsession error, identifying, by the gateway, a backup PCF associated witha different network generation than the primary PCF; sending, by thegateway, the CCR to the backup PCF over a second Gx interface; andreceiving, by the gateway, a Credit Control Answer (CCA) from the backupPCF over the second Gx interface confirming that Gx session binding hasbeen established for the UE between the gateway and the backup PCF,wherein: the gateway is a Long Term Evolution (LTE) Packet Data NetworkGateway (P-GW), the primary PCF is an LTE Policy and Charging RulesFunction (PCRF), and the backup PCF is a 5G PCF, or the gateway is a 5GUser Plane Function (UPF), the primary PCF is a 5G PCF, and the backupPCF is a LTEP CRF.
 2. (canceled)
 3. (canceled)
 4. The method of claim 1,further comprising receiving, by the gateway, Policy and ChargingControl (PCC) rules from the backup PCF via the second Gx interface, thePCC rules being applicable to a communication session requested by theUE.
 5. The method of claim 1, wherein detecting the Gx session errorassociated with the primary PCF comprises tracking a rate of CCRs sentto the primary PCF that did not result in Gx sessions being establishedbetween the gateway and the primary PCF, and wherein the gatewayidentifies the backup PCF in response to detecting the Gx session errorwhen the rate exceeds a threshold rate.
 6. The method of claim 1,wherein detecting the Gx session error associated with the primary PCFcomprises determining that a timeout error has occurred when the primaryPCF does not respond to the CCR within a predetermined period of time.7. The method of claim 1, further comprising: receiving, by a IPMultimedia Subsystem (IMS) element, a message from the UE requestinginitiation of a communication session for the UE; sending, by the IMSelement, an Authorize/Authenticate Request (AAR) associated with thecommunication session for the UE to the primary PCF over a first peer Rxinterface; detecting, by the IMS element, a Gx binding unavailable errorassociated with the primary PCF; sending, by the IMS element, the AAR tothe backup PCF over a second peer Rx session; and receiving, by the IMSelement, an Authorize/Authenticate Answer (AAA) from the backup PCF overthe second peer Rx session confirming that the backup PCF identified Gxbinding information associated with the Gx session binding.
 8. Themethod of claim 7, wherein detecting the Gx binding unavailable errorassociated with the primary PCF comprises receiving, by the IMS element,a Diameter message over the first peer Rx session indicating that theprimary PCF could not find Gx binding information associated with theUE.
 9. A gateway of a telecommunication network, comprising: one or moreprocessors; and memory storing computer-executable instructions that,when executed by the one or more processors, cause the gateway to: senda Credit Control Request (CCR) associated with a user equipment (UE) toa primary Policy Control Function (PCF) over a first Gx interface;detect a Gx session error associated with the primary PCF indicatingthat a Gx session has not been established between the gateway and theprimary PCF; in response to detection of the Gx session error, identifya backup PCF associated with a different network generation than theprimary PCF; send the CCR to the backup PCF over a second Gx interface;and receive a Credit Control Answer (CCA) from the backup PCF over thesecond Gx interface confirming that Gx session binding has beenestablished for the UE between the gateway and the backup PCF, wherein:the gateway is a Long Term Evolution (LTE) Packet Data Network Gateway(P-GW), the primary PCF is an LTE Policy and Charging Rules Function(PCRF), and the backup PCF is a 5G PCF, or the gateway is a 5G UserPlane Function (UPF), the primary PCF is a 5G PCF, and the backup PCF isa LTE PCRF.
 10. (canceled)
 11. (canceled)
 12. The gateway of claim 9,wherein the computer-executable instructions further cause the gatewayto receive Policy and Charging Control (PCC) rules from the backup PCFvia the second Gx interface, the PCC rules being applicable to acommunication session requested by the UE.
 13. The gateway of claim 9,wherein detection of the Gx session error associated with the primaryPCF comprises tracking a rate of CCRs sent to the primary PCF that didnot result in Gx sessions being established between the gateway and theprimary PCF, and wherein the gateway identifies the backup PCF inresponse to detecting the Gx session error when the rate exceeds athreshold rate.
 14. The gateway of claim 9, wherein detection of the Gxsession error associated with the primary PCF comprises determining thata timeout error has occurred when the primary PCF does not respond tothe CCR within a predetermined period of time.
 15. One or morenon-transitory computer-readable media storing computer-executableinstructions that, when executed by one or more processors of a gatewayof a telecommunication network, cause the gateway to perform operationscomprising: sending a Credit Control Request (CCR) associated with auser equipment (UE) to a primary Policy Control Function (PCF) over afirst Gx interface; detecting a Gx session error associated with theprimary PCF indicating that a Gx session has not been establishedbetween the gateway and the primary PCF; in response to detecting the Gxsession error, identifying a backup PCF associated with a differentnetwork generation than the primary PCF; sending the CCR to the backupPCF over a second Gx interface; and receiving a Credit Control Answer(CCA) from the backup PCF over the second Gx interface confirming thatGx session binding has been established for the UE between the gatewayand the backup PCF, wherein: the gateway is a Long Term Evolution (LTE)Packet Data Network Gateway (P-GW), the primary PCF is an LTE Policy andCharging Rules Function (PCRF), and the backup PCF is a 5G PCF, or thegateway is a 5G User Plane Function (UPF), the primary PCF is a 5G PCF,and the backup PCF is a LTE PCRF.
 16. (canceled)
 17. (canceled)
 18. Theone or more non-transitory computer-readable media of claim 15, whereinthe operations further comprise receiving Policy and Charging Control(PCC) rules from the backup PCF via the second Gx interface, the PCCrules being applicable to a communication session requested by the UE.19. The one or more non-transitory computer-readable media of claim 15,wherein detecting the Gx session error associated with the primary PCFcomprises tracking a rate of CCRs sent to the primary PCF that did notresult in Gx sessions being established between the gateway and theprimary PCF, and wherein the gateway identifies the backup PCF inresponse to detecting the Gx session error when the rate exceeds athreshold rate.
 20. The one or more non-transitory computer-readablemedia of claim 15, wherein detecting the Gx session error associatedwith the primary PCF comprises determining that a timeout error hasoccurred when the primary PCF does not respond to the CCR within apredetermined period of time.